Spectacle of Lights - PLSN.com

Taking the
VIDEO DIGERATI
Frame Blender
Off “Choppy”
By VickieClaiborne
Many media servers feature a control
channel for Media Play Speed. How
does this feature affect your content?
Have you ever used it? Well, if you have, you
will very quickly know whether or not that media
server uses frame interpolation, also called
frame blending or video smoothing.
When a piece of content is created, it will
be rendered at a specific speed in frames per
second, or FPS. Typically, that value will be15,
25, 29 or 30 FPS, depending on the format of
the media, the codec and even the hardware
being used for playback. If a piece of video
The result made lighting
designers cringe.
content is rendered at 30 FPS, what happens
when you use the Play Speed control channel
and slow the movie down? That actually
depends on the software and media server.
When a piece of 30 FPS content is being
played back at its rendered speed, all will appear
normal, and each frame will blend cohesively
into the next. But when that same piece
of content is played back at 15 FPS (overriding
the content’s rendered frame rate via
the Play Speed control channel), the content
will be playing back at half of its rendered
speed, and it can appear “jerky” or “choppy”
because you have time-stretched the
footage — that is, unless the software can “ fill in
the missing frames,” which is the effect of frame
interpolation.
How Does Frame Interpolation Work? PC
Frame interpolation is the process of creating
intermediate video frames based on the
data in two consecutive frames of encoded
video. Technically, pixels are displaced by
mixing pixels from the source in the current
frame with source pixels from previous or future
frames. Basic frame blending is used to
compute intermediate pixels and to produce
anti-aliased results in the render. In effect,
frame interpolation
increases the frame
rate of encoded video
at the time of decoding.
Essentially, the
content is rendered
with a codec, or compression/decompression
information. The decoders in the media server’s
software can compare the information in
the frames of the movie and interpolate the
differences between them, thereby filling in
what is missing. The algorithms being applied
by the decoders compensate and estimate
the motion and smoothing, which creates
smoother motion at slower FPS values. These
algorithms also do not involve any special encoding
options; this means that they do not
add any overhead to the content, and won’t
make your content larger.
In the lighting world, we are very accustomed
to being able to increase or decrease
the speeds of our effects with a control channel
without compromising the smoothness
of the effect. Rotating a gobo is just one example,
as are pan & tilt. Remember when you
would program an 8-bit pan/tilt fixture on
a DMX console and try using a really slow
fade time? The result made lighting designers
cringe. As a result of that feedback from
designers, the manufacturers of intelligent
lighting fixtures soon doubled the number of
pan & tilt channels and increased the resolution
of a pan/tilt crossfade to 16-bit, and we
suddenly went from a mere 256 bits of data
in a crossfade to 65,536 bits of data in a crossfade.
Once that change occurred, pan and tilt
smoothness during a slow crossfade quickly
became the signature of a quality automated
lighting fixture, and all manufacturers followed
suit by offering full and reduced resolution
modes for their fixtures.
Now, here we are in a lighting world that
is quickly converging with the video world,
but we lighting designers and programmers
expect the same results from our digital lighting
fixtures that we already get from our automated
lighting fixtures. Thus, manufacturers
of media servers are being pressed to make
improvements in order to match our expectations.
A media server that offers frame blending
has the benefit of being able to generate
higher quality slow-motion video since it
“inserts” newly interpolated frames into any
gaps between frames, which we perceive as
spatial motion smoothing. This is where companies
like Green Hippo are leading the way,
with their latest version of the Hippotizer.
I had the opportunity to sit with the developers
of The Hippotizer while at LDI in
October to check out their latest version
of software, v3. This version of their media
server has an extremely well designed frame
blending feature that makes content appear
remarkably smooth at really low frame
rates, and this makes it an incredibly powerful
digital lighting tool. It is also one of the first
digital lighting media servers to make use of
a frame interpolation technique to produce
these impressive results. In fact, it does interpolation
so well that it is next to impossible
to tell that the content was not created at the
lower frame rate. I believe that all media servers
will need to perform at this level if they
want to be competitive at the pro level, because
products like the Hippotizer, with it’s
ease of use and powerful playback capabilities,
will keep raising the bar. Advancements
in new technology and hardware, along with
the development of new software that makes
use of those technological improvements,
contribute to increased performance capabilities
of our media servers, and they will only
continue to shape the future of our digital
lighting world.
Vickie Claiborne (www.vickieclaiborne.com)
is an independent programmer and training
consultant, and can be reached at vclaiborne@plsn.com.
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PLSN DECEMBER 2006 41